The twisted relation between Pnu and SWEET transporters

Jaehme, Michael; Guskov, Albert; Slotboom, Dirk Jan

doi:10.1016/j.tibs.2015.02.002

Cited by 14 publications

(21 citation statements)

References 41 publications

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“…6a). Together, the membrane topology of SWEET shows drastically different connectivity and spatial TM arrangement when compared to other known heptahelical membrane proteins, in particular G-protein coupled receptors or PnuC vitamin transporters 17-19 (Extended Data Fig. 7).…”

mentioning

confidence: 97%

Structure of a eukaryotic SWEET transporter in a homotrimeric complex

Tao

Cheung

et al. 2015

Nature

159

221

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Eukaryotes rely on efficient distribution of energy and carbon skeletons between organs in the form of sugars. Glucose in animals and sucrose in plants serve as dominant distribution forms. Cellular sugar uptake and release require vesicular and/or plasma membrane transport proteins. Humans and plants use related proteins from three superfamilies for sugar translocation: the major facilitator superfamily (MFS), the sodium solute symporter Family (SSF; only animal kingdom), and SWEETs1-5. SWEETs carry mono- and disaccharides6 across vacuolar or plasma membranes. Plant SWEETs play key roles in sugar translocation between compartments, cells, and organs, notably in nectar secretion7, phloem loading for long distance translocation8, pollen nutrition9, and seed filling10. Plant SWEETs cause pathogen susceptibility by sugar leakage from infected cells3,11,12. The vacuolar AtSWEET2 sequesters sugars in root vacuoles; loss-of-function increases susceptibility to Pythium infection13. Here we show that its orthologue, the vacuolar glucose transporter OsSWEET2b from rice, consists of an asymmetrical pair of triple-helix-bundles (THBs), connected by an inversion linker helix (TM4) to create the translocation pathway. Structural and biochemical analyses show OsSWEET2b in an apparent inward (cytosolic) open state forming homomeric trimers. TM4 tightly interacts with the first THB within a protomer and mediates key contacts among protomers. Structure-guided mutagenesis of the close paralogue SWEET1 from Arabidopsis identified key residues in substrate translocation and protomer crosstalk. Insights into the structure-function relationship of SWEETs is valuable for understanding the transport mechanism of eukaryotic SWEETs and may be useful for engineering sugar flux.

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mentioning

confidence: 97%

Structure of a eukaryotic SWEET transporter in a homotrimeric complex

Tao

Cheung

et al. 2015

Nature

159

221

View full text Add to dashboard Cite

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“…In this case the generation of a central linker TMH would be a sign of a constraint to conserve function, by inverting an "inverted topology". Inversion scenarios and comparisons of 3TMH protodomains have been reviewed extensively (Feng and Frommer, 2016;Jaehme et al, 2015;Xu et al, 2014). More recently it has been proposed from phylogenetic analyses that the eukaryotic SWEET protodomains may not have evolved by tandem duplication of an open reading frame, but rather originated by fusion between an archaeal and a bacterial SemiSWEET.…”

Section: Multi-level Symmetries In Sweet and Pnucmentioning

confidence: 99%

“…From the very simple schematic representations used in Figure 2.B , one can align TM1-TM6-TM7 and TM5-TM2-TM3 to SWEET/SemiSWEET 3TMH with a high structural homology (low RMSD). This is equivalent to a symmetric structural swap of TM1/TM5 as proposed (Jaehme et al, 2015), as sugar transporters PnuC and SWEET have effectively been proposed to be evolutionary related. PnuC is seen as a "full length" SWEET homolog (Feng and Frommer, 2016;Jaehme et al, 2014Jaehme et al, , 2015Jaehme et al, , 2016.…”

Section: Multi-level Symmetries In Sweet and Pnucmentioning

confidence: 99%

“…This is equivalent to a symmetric structural swap of TM1/TM5 as proposed (Jaehme et al, 2015), as sugar transporters PnuC and SWEET have effectively been proposed to be evolutionary related. PnuC is seen as a "full length" SWEET homolog (Feng and Frommer, 2016;Jaehme et al, 2014Jaehme et al, , 2015Jaehme et al, , 2016. This is in line with a survey (Murzin, 1998) on divergent structural folds, where the author notes: "... A simple way of altering a protein fold without a big destabilization is to change its topology while maintaining its architecture.…”

Section: Multi-level Symmetries In Sweet and Pnucmentioning

confidence: 99%

“…i.e., are they derived from a common ancestor, the same protosequence ? A domain swap has been hypothesized as a possible conformational transition at the protodomain level to reconcile different topologies of the three helices (Jaehme et al, 2014(Jaehme et al, , 2015(Jaehme et al, , 2016. Another study goes further and groups SWEETs, PnuC, and GPCRs into a "transporter-opsin-GPCR" (TOG) superfamily (Yee et al, 2013).…”

Section: Gpcrs Vs Pnuc: Are They Related?mentioning

confidence: 99%

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7-Transmembrane Helical (7TMH) Proteins: Pseudo-Symmetry and Conformational Plasticity

Youkharibache

Tran

Abrol

2018

Preprint

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Substrate selectivity and unique sequence signatures in SWEET/semiSWEET homologs of four taxonomic groups: Sequence analysis and phylogenetic studies

Gupta,

Sankararamakrishnan

2024

Proteins

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The recently discovered SWEET (Sugar Will Eventually be Exported Transporter) proteins are involved in the selective transport of monosaccharides and disaccharides. The prokaryotic counterparts, semiSWEETs, form dimers with each monomer forming a triple‐helix transmembrane bundle (THB). The longer eukaryotic SWEETs have seven transmembrane helices with two THBs and a linker helix. Structures of semiSWEETs/SWEETs have been determined experimentally. Experimental studies revealed the role of plant SWEETs in vital physiological processes and identified residues responsible for substrate selectivity. However, SWEETs/semiSWEETs from metazoans and bacteria are not characterized. In this study, we used structure‐based sequence alignment and compared more than 2000 SWEET/semiSWEETs from four different taxonomic groups. Conservation of residue/chemical property was examined at all positions. Properties of clades/subclades of phylogenetic trees from each taxonomic group were analyzed. Conservation pattern of known residues in the selectivity‐filter was used to predict the substrate preference of plant SWEETs and some clusters of metazoans and bacteria. Some residues at the gating and substrate‐binding regions, pore‐facing positions and at the helix–helix interface are conserved across all taxonomic groups. Conservation of polar/charged residues at specific pore‐facing positions, helix–helix interface and in loops seems to be unique for plant SWEETs. Overall, the number of conserved residues is less in metazoan SWEETs. Plant and metazoan SWEETs exhibit high conservation of four and three proline residues respectively in “proline tetrad.” Further experimental studies can validate the predicted substrate selectivity and significance of conserved polar/charged/aromatic residues at structurally and functionally important positions of SWEETs/semiSWEETs in plants, metazoans and bacteria.

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The twisted relation between Pnu and SWEET transporters

Cited by 14 publications

References 41 publications

Structure of a eukaryotic SWEET transporter in a homotrimeric complex

Structure of a eukaryotic SWEET transporter in a homotrimeric complex

7-Transmembrane Helical (7TMH) Proteins: Pseudo-Symmetry and Conformational Plasticity

Substrate selectivity and unique sequence signatures in SWEET/semiSWEET homologs of four taxonomic groups: Sequence analysis and phylogenetic studies

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